Detection or testing tubes are old and well known. Detector tubes are used, for example, with a pump means to draw ambient air or other gases or vapors through the tube to provide a colorimetric indication of the presence of a selected compound. A detector tube typically comprises an elongated glass tube adapted to attach at its exhaust end to a pump for drawing gas through the tube from its other end comprising the intake port. Both ends are sealed to protect the active components contained therein prior to use. Each detector tube includes a colorimetric indicating material which is specific to a particular gas, vapor, mist or reaction product.
Detector tubes have been provided for the detection of halogenated hydrocarbon compounds and are also well known. These tubes comprise a first layer (in the direction of gas flow) in which the halogenated hydrocarbon is cracked (dissociated) and a second layer consisting of an indicator material to detect dissociated halogen or a reaction product from the first layer. For example, a substance based upon permanganate-sulfuric acid has been utilized in the first layer to achieve a cracking of the halogenated hydrocarbon compound. While this material provides initially satisfactory results, the permanganate is subject to a gradual decomposition with the associated formation of inactive tetravalent manganese lead which reduces the cracking power of the first layer so that the detection becomes insensitive to small concentrations, i.e., in the range of a few ppm. Moreover, decomposition of the permanganate can take place prior to the use of the detection tube resulting in a detection tube with little shelf life or stability.
Other materials have been used, such as an oxidizing medium consisting of a granular support carrier impregnated with a solution of sulfuric acid and chromium trioxide. While first layer based on hexavalent chromium associated with sulfuric acid are stable in storage, their capability to dissociate a halogenated hydrocarbon to attain the sensitivity necessary to indicate concentration ranges of a few parts per million is generally inadequate.
Accordingly, it is an object of the present invention to provide a material for use in the first layer of a detection tube which is stable during storage and which at the same time provides a high degree of sensitivity to indicate halogenated hydrocarbons present in concentrations of a few parts per million. It is also an object of the present invention to provide a detector tube sensitive to the halogen derivatives of unsaturated hydrocarbons, and to a detector means in which the dissociation reaction and indication are carried on in separate, but joined tubes.